The present invention relates to refrigerant expansion valves and particularly valves employed for controlling flow of high pressure refrigerant from a condenser and expansion to a lower pressure and flow to an evaporator and is particularly suitable for such applications as motor vehicle passenger compartment air conditioning systems. Heretofore, refrigerant expansion valves employed for vehicle passenger compartment air conditioning have utilized either a fluid filled temperature responsive capsule for moving the expansion valve in response to temperature changes in the fluid in the capsule; or, the valves have employed a solenoid operator for linearly moving a poppet with respect to a valve seat for controlling flow through the valve high pressure inlet to the outlet at a substantially reduced pressure. Electrically operated valves are deemed preferable in motor vehicle passenger compartment air conditioning systems because the electronic controller provides more rapid response for the system.
However, known solenoid operated refrigerant expansion valves have proven to be somewhat unstable and difficult to modulate because a small amount of movement of the poppet results in a substantial change in flow; and, it is extremely difficult to provide fine resolution for the control of movement of a solenoid armature in order to achieve the desired modulation of the refrigerant flow from the valve inlet and across the valve seat to the valve outlet.
It has therefore been desired to provide a way or means of electrically operating a refrigerant expansion valve particularly for such valves employed in an air conditioning system for a motor vehicle passenger compartment in a manner which yields fine resolution of the flow and is relatively inexpensive to manufacture and is sufficiently robust for the environment of such applications.
The present invention provides a servo motor operated refrigerant expansion valve having a rotary motor, such as a stepper motor, mounted directly to the valve body with the motor shaft linearly moving a valve spool with a ball screw connection from the rotating motor shaft to the spool. The spool is slidably sealed in a valving bore and moveable therein with respect to an inlet and outlet port staggered along the valving bore. The valve body contains a separate sensing passage which is adapted for connection to receive flow therethrough from the evaporator returning to the compressor inlet; and, a temperature sensor, preferably a thermistor, is disposed in the sensing passage and connected to provide an electrical temperature signal indicative of refrigerant temperature to an electronic control unit which provides a drive signal for the valve motor.
The present invention thus provides a fine resolution of movement of the spool in the valving bore for modulating refrigerant flow between the inlet and the outlet of the valve. In a typical refrigeration system, the valve inlet is connected to receive the high pressure flow from the condenser and the valve outlet discharges to the evaporator inlet at a substantially reduced pressure.